Inhibitor for metal pickling baths



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Patented Aug. 28, 1934 UNITED STATES PATENT; OFFICE INHIBITOR FOR METAL PICKLING BATHS No Drawing. Application September 2, 1931, Serial No. 560,878

10 Claims.

The present invention relates to the cleaning of metallic surfaces, and particularly to a new class of inhibitors, which are employed to prevent undue attack upon the surface of a metal when in contact with a pickling bath of an acid nature.

More specifically, some of the objects of the invention are to obviate over-pickling, embrittlement and pitting of the articles treated; to minimize the amount of metal lost in pickling; to increase the efficiency of the pickling operation; to prolong the effective life of the pickling bath; and particularly to facilitate the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

In the art of pickling, the metal is treated with a dilute acid to remove oxides such as rust, scale and other deposits, after which the metal is preferably washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid removes the rust and scale, but unfortunately, from the pickling standpoint, unless some agent to prevent such action is present, it attacks the cleaned metal itself, thereby causing loss of metal and producing an evolution of hydrogen gas, which escapes into the air, carrying with it a fine spray of the acid liquor from the pickling bath and producing an atmos phere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a minimum. 'Io accomplish to as great an extent as possible the objects set forth in accordance with the present invention, there is added to the pickling bath an inhibitor or regulating agent which acts to restrain the action of the acid from attacking clean metal but assists in removing the rust, scale and other deposits, or, in other words, the inhibitor causes the acid selectively to remove such materials without appreciably attacking the clean portions of the metal under treatment.

In the examples hereinafter set forth for carrying out the metal pickling process, conditions were imposed which duplicated, so far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed.

The new class of pickle regulators or inhibitors, as disclosed in the present application, comprises xanthane hydride and analogous compounds possessing a five-membered ring nucleus comprising two atoms of carbon, two atoms of sulfur and one atom of nitrogen.

One of the preferred class of compounds, for example, xanthane hydride, was prepared by the action of an acid upon a thiocyanate, preferably by the action of hydrochloric acid upon ammonium thiocyanate in an aqueous solution. (Cf. Beilsteins Handbuch der Organischen Chemie, 3rd. ed., Vol. I, p. 1286.) It is believed (cf. Chemisches Centralblatt, 1904, II, p. 31) that this compound possesses the structure A portion of this compound was incorporated in a pickling bath and its value as an inhibitor determined in the following manner: A test piece of 28 gauge hot rolled tin plate steel stock, approximately 4" x 3" in dimension, was immersed in the pickling bath, comprising substantially 750 c. c. of a water solution containing approximately 6% by weight of 66 B. sulfuric acid and 0.070 grams of the inhibitor above described. The temperature of the bath was maintained at from to c. The steel test piece weighed 17.023 80 grams before immersion in the bath, and after 40 minutes pickling weighed 17.014 grams, showing thereby a loss of only 0.009 grams. A similar test piece weighing 18.499 grams and treated in the same manner, but without the use of any in- 35 hibitor, lost 0.519 grams. Thus it is shown that when one of the preferred class of inhibitors, for example, xanthane hydride, is employed as an inhibitor, the loss in weight per square inch of surface exposed corresponds to 0.00038 grams, whereas when no inhibitor is employed in the test described, the loss per square inch of surface exposed corresponds to 0.02163 grams. The loss in weight per square inch of surface exposed is only 1.8 percent as great by employing the inhibitor set forth as results if no inhibitor is employed in the pickling process. A greater saving in metal losses results from the use of a larger amount of the inhibitor than that employed in the example. Moreover, the steel plates pickled in the presence of the inhibitor set forth are clean and not stained upon removal from the pickle bath.

As further examples of the new class of materials the following analogues of xanthane hydride have also been tested as inhibitors. Thus, the following compounds were tested in a pickling bath in the manner hereinbefore described:

Compound A.-Thiuret hydroiodide, which was prepared by reacting xanthane hydride with ani- 11 line, and further reacting the phenyl-dithiobiuret thus formed with iodine. (Cf. Beilstein, Vol. II, pp. 399 and 401.) This compound is believed to possess the structure the structure Compound C'.Persulfocyanglycollic acid, which was prepared by reacting the sodium salt of xanthane hydride with sodium chloracetate and treating the sodium salt thus formed with hydrochloric acid. (Cf. Beilstein, Vol. I, p. 1287.) It is believed that this compound possesses the structure Compound D.Reaction product of xanthane hydride and benzoyl chloride. This product was formed by heating together substantially two molecular proportions of benzoyl chloride and substantially one molecular proportion of xanthane hydride at a temperature of approximately 120 to 130 C. for a suitable period of time necessary to complete the reaction, preferably for a period of approximately four hours. The resulting product was washed free of any unreacted benzoyl chloride.

The results of the tests obtained on immersing steel test strips of 28 gauge hot rolled tin plate stock, 3" x 4" in dimension, for 40 minutes in 750 c. c. of 6% by weight of 66 B. sulfuric acid at C., in the presence of the indicated quantity of one of the above described inhibitors, are given in Table I.

Table I Inhlbiting compound employed It is apparent from the data set forth that the preferred class of materials constitutes an important and highly efiicacious group of inhibitors, as in all cases wherein one of the preferred inhibiting compounds was incorporated in the pickle liquor there resulted a great saving in.the loss in weight of the steel test strips as compared with that resulting when no inhibitor was employed.

Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling of metals are apparent to those skilled in the art to which this invention pertains. The prodm group consisting of an aliphatic carboxylic acid ucts described additionally may be employed in the presence of foaming agents, ionizable substances or other materials ordinarily used. Again, other acids than sulfuric acid may be employed in the pickle bath. Thus, hydrochloric acid as well as other inorganic acids may be employed in the pickle bath in conjunction with the preferred class of inhibitors in the manner hereinbefore set forth.

What is claimed is:

1. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a member of a group of compounds consisting of thiuret hydroiodide, acetyl xanthane hydride, persulfocyanglycollic acid and the reaction product of substantially two molecular proportions of benzoyl chloride and substantially one molecular proportion of xanthane hydride.

2. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a member of a group of compounds consisting of thiuret hydroiodide, acetyl xanthane hydride, persulfocyanglycollic acid and the reaction product of substantially two molecular proportions of benzoyl chloride and substantially one molecular proportion of xanthane hydride.

3. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of xanthane hydride possessing an acyl substituent.

4. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of xanthane hydride possessing an acetyl substituent.

5. A pickling bath for metal products which 1 comprises a mineral acid solution containing a small proportion of xanthane hydride possessing an acyl substituent.

6. A pickling bath for metal products which comprises a mineral acid solution containing a 2 small proportion of xanthane hydride possessing an acetyl substituent.

'7. A process of pickling metal products which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of a compound of the structure where R represents one member of a group consisting of hydrogen and an aliphatic carboxylic acid residue and R1 represents one member of a residue and an acyl radical.

8. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of a compound of the structure vvl'l uul l IUIIO,

comprises a mineral acid solution containing a small proportion of a compound of the structure ing a small proportion of a compound of the structure where R represents one member of a group consisting of hydrogen and the radical HOOC.CH2 and R1 represents one member of a group consisting of the radical HOOCCHaand an acyl radical.

DEAL H. TOMPKINS.

examine; 

